1. Field of the Invention
This invention relates generally to transparent multilayer containers; specifically, to transparent multilayer containers having a layer of polypropylene and a layer of a barrier material which provides oxygen, carbon dioxide and moisture protection.
2. Background Art
Many products that can be filled and stored in plastic containers require carbon dioxide, oxygen and moisture barrier protection to keep the products fresh for extended periods of time. Such products include, by way of example only, certain carbonated beverages, fruit juices, beer, sauces, ketchup, jams, jellies and dry foods such as instant coffee and spices. Most commercially acceptable transparent multilayer containers that provide carbon dioxide and oxygen barrier protection are made of at least one layer comprising a polyester such as polyethylene terephthalate (xe2x80x9cPETxe2x80x9d) and a layer comprising ethylene vinyl alcohol copolymer (xe2x80x9cEVOHxe2x80x9d). The layer of EVOH in such containers provides excellent carbon dioxide and oxygen barrier protection. EVOH can also act as a chemical or fragrance barrier to keep flavors fresh for various products such as orange juice.
PET has limited moisture barrier protection compared with polypropylene. As a result, liquid products stored in PET containers experience moisture loss resulting in product weight loss and dry products stored in PET containers absorb more moisture than products stored in polypropylene containers. In addition, PET bottles have limited hot fill capabilities due to a low glass transition temperature of PET. Additionally, the injection molding process temperatures of PET and EVOH are significantly different thus creating difficulties in molding these two materials together in, for instance, multi-layer injection molding systems.
It is known to use polypropylene, instead of PET, for an inner and outer layer of multi-layer containers in extrusion blow molding applications. One advantage of polypropylene over PET is that polypropylene provides containers with better hot fill properties. Furthermore, polypropylene and EVOH have relatively similar melting temperatures, which makes it easier to maintain proper injection molding or extrusion molding systems.
Unfortunately, however, polypropylene does not bond to EVOH without the assistance of an additional agent. As a result, known containers made with polypropylene and EVOH require a layer of an adhesive between each layer of polypropylene and the layer of EVOH. Accordingly, multilayer polypropylene containers with carbon dioxide and oxygen barrier protection have typically had at least five layers of material: a first layer of polypropylene, a first layer of adhesive, a layer of EVOH, a second layer of adhesive and a second layer of polypropylene.
Additionally, known polypropylene containers with barrier protection have haze values of approximately 29%-35% or greater. While it is known to injection stretch blow mold containers with a single layer of clarified polypropylene to make a transparent bottle having lower haze values, such containers do not have many commercial purposes for food applications because they do not provide significant carbon dioxide or oxygen barrier protection.
The transparent containers of the present invention have a layer comprising polypropylene and a layer comprising a barrier material such as ethylene vinyl alcohol copolymer, nylon or a blend of ethylene vinyl alcohol copolymer and nylon, adjacent to the polypropylene layer wherein at least one of the polypropylene layer and the barrier layer comprises an adhesive mixed therein.
It is one of the principal objectives of the present invention to provide multilayer plastic containers that also provide oxygen, carbon dioxide and moisture barrier protection having a haze value of less than 25%.
It is another object of the present invention to provide containers having a layer of a polypropylene/adhesive mixture and a layer of barrier material directly adjacent the layer of polypropylene/adhesive mixture.
It is another object of the present invention to provide containers having a layer of a polypropylene and a layer of barrier material/adhesive mixture directly adjacent the layer of polypropylene.
It is another object of the present invention to provide commercially acceptable, cost effective containers having a layer comprising polypropylene and a layer comprising a barrier material adjacent to the polypropylene layer, wherein the containers may be used for carbonated beverages, fruit juices, sauces and beer.
It is still another object of the present invention to provide a polypropylene bottle having at least two layers and having a haze value of less than 25%.
It is further an object of the present invention to use two different materials with similar melting temperature to provide more compatible injection molding systems.